FIG. 5 shows a circuit diagram of a conventional valve apparatus used as a load valve for loading an accumulator. The reference character S indicates the hydraulic accumulator, which is supplied with hydraulic fluid via a restrictor D and a check valve RV. Reference character N indicates a consuming unit which can be supplied with hydraulic fluid via a control valve SV. In addition, hydraulic pressure is applied to the control line SL via the restrictor D and the regulating valve REV. The regulating valve REV is "tensioned" by the hydraulic pressure in the control line SL. The regulating valve REV has three positions, A, B, and C. In FIG. 5, the regulating valve REV is shown in position A. In position A, the hydraulic pressure is applied from pump P to control line SL via the restrictor D. In position B, all ports of the regulating valve REV are closed off, and in position C the control line is discharged into tank T.
As indicated in FIG. 5, the regulating valve is tensioned on both sides by the hydraulic pressure in the control line SL; plunger K1 (on the right side in FIG. 5), which tries to force the regulating valve REV into discharge position C, has a smaller area than the opposing plunger K2. A further plunger K3, to which the pressure of the accumulator S is applied, acts on the right side of the regulating valve REV. Plunger K3 also tries to force the regulating valve into discharge position C. A spring F on the left side of the regulating valve opposes plunger K3 and plunger K1, and spring F is assisted by plunger K2. The pressure line SiV on the left of the selector valve serves as the signal pressure line of the consuming device V.
The loading procedure for the accumulator S is described below. The control valve SV is only used to control hydraulic flow to the consuming device N and has no effect on the loading procedure. The control valve SV is closed during the loading procedure and therefore has no function with respect to the loading procedure.
During the loading procedure, plunger K2 balances out the load applied by plunger K3. Thus only plunger K1 opposes spring F. At the end of the loading procedure, plungers K1 and K2 are released; and plunger K3 then suddenly acts on spring F, leading to an abrupt control movement (load, deflection or hysteresis). If the accumulator S is empty or mostly empty, the regulating valve REV is in position A as shown. The accumulator V is loaded "slowly" in this position via the restrictor D and the check valve RV. If the accumulator S reaches a given pressure, plunger K1 forces the regulating valve REV into position B. As already explained, plungers K2 and K3 balance out each other's load during the loading procedure, such that the regulating valve REV is forced into position B. As a result, the dynamics of the system create an intermediate position A/B. When the pressure line is discharged into tank T, the pressure in plungers K1 and K2 drops to the level in the tank. As a result, only plunger K3 continues to have an effect. The abrupt change in load on the plunger results in an abrupt change in the deflection of the plunger, with approximately 18% hysteresis.
The pressure level at which the regulating valve is moved can be set via spring F. In position B, the pressure which has already built up in the control line SL is held, and the pump supplies further hydraulic fluid. If the pressure in accumulator S increases further, the regulating valve REV is forced into position C. In this position, the pressure from the control line is released into the tank. When the pressure in the control line drops abruptly, pump P receives a signal to go to idle if the loading pressure is the highest pressure in the load valve apparatus.
If the pressure in accumulator S drops, the reverse takes place. The regulating valve is forced back into position C by spring F. In this position, pressure can once again build up in the control line SL, since the pump is operating at idle. Once the pressure reaches a certain level, a signal is sent to the pump to increase its pumping rate to full. A short circuit at the regulating valve causes deactivation of the pump; otherwise, the pressure rises until the delta P of the regulating valve for a pumping rate greater than zero is reached. This loading apparatus has certain disadvantages, however. The accumulator S continues to be loaded until the pump P is deactivated. If consuming devices in V are loaded to a pressure that is higher than the deactivation pressure of the load valve apparatus, the accumulators will be loaded up to that pressure. If the load pressure exceeds the maximum permitted accumulator pressure, the accumulator S or the valve will be overloaded.
The object of the invention is to produce a load valve apparatus which keeps the accumulator S and the valve (whose housing is generally made of grade GG 30 gray cast iron) from overloading.